Modern utility-scale wind turbines utilise wind turbine blades of relatively large size, often exceeding 40 meters in length. Such blades are mostly manufactured using fibre-composite materials, which comprise a fibre, e.g. fibreglass, carbon fibres, held in a cured resin. One common manufacturing process used in the construction of these blades is the moulding of separate sections or shells of a wind turbine blade in separate moulds, the different sections or shell subsequently assembled together to form a complete wind turbine blade.
Often, such blade sections will be assembled having an internal spar element, e.g. a spar box or a shear web, extending between opposed blade sections, the spar element providing shear strength and reinforcement to the wind turbine blade structure.
With reference to FIG. 1, a cross-sectional illustration is provided of a joining between a portion of a blade shell or section 110 and an internal spar element, in this case an I-shaped shear web 112. The I-web 112 comprises a joining surface 114 which is arranged to bond to a corresponding joining surface 116 provided on the blade shell 110. A portion of resin or adhesive 118 is provided on the joining surface 114, and the I-web 112 is applied against the surface 116 of the blade shell 110, such that the adhesive 118 spreads between the two surfaces 114,116 to bond the shear web 112 to the blade shell 110.
However, this approach can often present subsequent problems during blade operation. With reference to FIG. 2, an example is illustrated of the system of FIG. 1 after curing of the adhesive 118 into an adhesive bonding layer 120 between the I-web 112 and the blade shell 110. In a first aspect, the bonding layer 120 is one of the most likely locations for subsequent blade failure, due to the increased possibility of crack formation at the interface between the adhesive bond layer 120 and the blade shell, indicated at 122.
A further drawback of the approach adopted in FIG. 1 is that it is difficult to guarantee that the adhesive 118 will spread evenly between the joining surfaces 114,116. This may be as a result of an uneven initial application of adhesive to the first joining surface 114, and/or the first joining surface being pressed towards the second joining surface 116 at an angle, resulting in an uneven distribution of pressure forces.
In the example shown in FIG. 2, the adhesive 118 has not fully spread between the joining surfaces 114,116, resulting in the formation of an adhesive bonding layer 120 which does not extend across the full extent of the space between the joining surfaces 114,116, indicated by empty space 124 defined between the joining surfaces 114,116. As a result, the strength of the adhesive bond between the joining surfaces 114,116 is reduced, which may lead to bond failure between the blade components 110,112.
To avoid such a failure, blade designers often adopt at least one of the following approaches. Firstly, adhesive 118 can be applied in a quantity considerably in excess of what is sufficient to fill the space between the joining surfaces 114,116, with the hope that such an excess amount will ensure that the area between the joining surfaces 114,116 is filled with adhesive. However, this approach leads to a wasteful use of adhesive during blade manufacture. Additionally, any excess adhesive which cures outside of the area between the joining surfaces 114,116 will often break away some time subsequent to curing, resulting in loose debris within the interior of a wind turbine blade. Finally, the use of such an excess quantity of adhesive does not completely guarantee that the area between the joining surfaces 114,116 will be filled with adhesive, as additional factors such as the direction in which pressure is applied to the I-web 112 when joining to the blade shell 110 may still result in an uneven application of adhesive between the joining surfaces 114,116.
A second approach is that the blade components, in particular spar elements such as I-web 112, are designed to be over dimensioned, such that the structural integrity of the wind turbine blade is not significantly compromised in the event that the adhesive layer 120 does not extend across the entire extent of the area between the joining surfaces 114,116. However, this over-dimensioning approach results in an inefficient use of resources, and increases the cost and weight of the wind turbine blade.
Finally, wind turbine manufacturers can decide to survey the adhesive layer 120 between the joining surfaces 114,116 after curing of the adhesive 118, to ensure that there is an adequate bond between components 110,112. In the event of an incomplete bond, a subsequent repair operation can be performed, through the application of additional adhesive to the affected area. However, such an approach can be relatively costly and time-consuming, in particular when it has to be carried out on a closed wind turbine structure, where the surveying and subsequent repair operations must be carried out from the exterior of the blade, e.g. using ultrasonic detection to identify the size of adhesive bond layers 120, and pumping additional resin or adhesive from the exterior of the blade to the interior to provide for adequate bonding.
US Patent Application Publication No. US 2012/0114497 discloses the use of a resin barrier applied to a joining surface between members of a wind turbine blade, to define a cavity between the blade members. Resin can them be pumped into said cavity, to ensure that the adhesive fully fills the defined cavity between the members. However, this approach requires considerable additional preparation during blade manufacture, in the accurate placement of the resin barrier as well as the subsequent pumping of adhesive into the defined cavity, thereby increasing the complexity and time of the manufacturing process. Furthermore, this system does not address the problem of bonding failure at the interface of adhesive joints between the blade members.
US 2012/0027613 and US 2012/0027610 disclose spring flange members as part of a connection assembly between transverse ends of a shear web and a spar cap.
Accordingly, it is an object of the invention to provide a method of manufacturing a wind turbine blade, in particular a method of joining two wind turbine blade components, which provides for improved reliable bonding between components balanced with a relatively simple implementation, compared to prior art systems.